S. Joglekar1, J. C. Lee1,2, J. Serpell1,2, H. Schneider3 1The Alfred Hospital,Department Of General Surgery,Melbourne, VICTORIA, Australia 2Monash University,Endocrine Surgery Unit,Melbourne, VICTORIA, Australia 3The Alfred Hospital,Department Of Pathology (Clinical Biochemistry),Melbourne, VICTORIA, Australia
Introduction:
Inappropriately high serum parathyroid hormone (PTH) is a diagnostic criterion for primary hyperparathyroidism (pHPT). Recently hospital administrative records showed an increase in the diagnosis of pHPT during a 2-year (approx.) period when the Abbott assay was used instead of the usual Roche assay for our institution due to product unavailability. Therefore, we aimed to compare the clinical performance of these 2 2nd generation assays in patients undergoing parathyroidectomy for pHPT.
Methods:
All study patients underwent parathyroidectomy for pHPT at The Alfred Hospital. Those who were treated during the 20-month period (May 2012 to Feb 2014 inclusive) when the Abbott assay was in use were designated “Group A”; and those treated during the subsequent 20-month period (Mar 2014 to Dec 2015 inclusive) when the Roche assay was again in use were designated “Group R”. Comparisons were made of their biochemistry (serum calcium, PTH, vit D levels), as well as clinical outcomes (diagnostic accuracy and recurrence prognostication), using the Student’s t-test and Fisher’s exact test. Deviation of PTH from normal ranges are expressed as multiples of the upper limit of normal (xULN), as the 2 assays have different normal ranges. A biochemical diagnosis was classified as false positive (FP) when associated with a negative neck exploration. Post-operative PTH reduction was calculated from pre-operative and recovery room PTH levels. In this study, curative treatment was defined as normo-calcaemia lasting over 3 months.
Results:
There were 79 patients in Group A and 64 in Group R. Mean ages and gender distribution were similar between the groups (63.3 ± 15.6 years vs 62 ± 12.9 years; 75% vs 70% female). The mean pre-operative PTH in Group A (2.25 ± 0.28 xULN) was significantly higher than in Group R (1.84 ± 0.25 xULN; p < 0.05); this was despite similar levels of hypercalcaemia (2.78 ± 0.17 mM vs 2.77 ± 0.18 mM respectively; p = 0.72). The FP rates were similar (p = 0.65), with each group only having 2 patients with a negative 4-gland exploration. Operative PTH reduction of > 50% was seen in the majority in both groups (Group A 92% vs Group R 93%), as was normo-calcaemia at 3 months (Group A 90% vs Group R 93%).
Conclusion:
This study confirmed that although the Abbott assay measured higher PTH levels in patients with pHPT compared to the Roche assay, this does not seem to affect the ability of these assays to make an accurate diagnosis. Furthermore, the comparable kinetics of post-operative PTH conferred similar medium term normo-calcaemia rates.